Bolton Council has said it has two “highly probable” cases of the mutation identified in its borough.
The local authority says these are yet to be confirmed by laboratories, but it has nevertheless acted swiftly in response to the information it has received.
The individuals that have tested positive are linked and members of their households are being re-tested and are self-isolating.
Contact tracing is under way and all contacts regardless of vaccine status are being followed up and requested to isolate and get tested.
Dr Helen Lowey, director of public health at Bolton Council, said: “Omicron is a new variant and we have more work to do to understand how easily this can be transmitted, and how well the vaccines work to protect against it.
“In the meantime, it is important that we all play our part to prevent transmission by remaining cautious and taking steps to keep COVID-safe, particularly at a time when our overall coronavirus rates are going up.
“Vaccination is critical to help us strengthen our defences against this new variant – please get your first, second or booster jab without delay.
“Wear a face covering in all enclosed spaces, including on public transport, shops and crowded places. Isolate immediately and get a PCR test if you have symptoms.
“Use a lateral flow test before socialising, and ideally test twice a week especially if going into workplaces or shopping, meet outdoors if you can as it is safer, and open a window to let in fresh air if you meet indoors. And if you can work from home, please do so.
“I urge everyone to look out for the ‘COVID’s Still Here’ campaign and follow the advice to help keep Bolton safe and to help keep everything open through the winter.”
On Wednesday, Lancashire County Council confirmed a case of the Omicron variant had been identified in Lancaster, and it was also detected in Liverpool on Monday.